wilmotte



Aug. 27, 1935.

R. M. WILMOTTE METHOD OF AND APPARATUS FOR LOCATING A POINT IN SPACEFiled June 26, 193C 2 Sheets-Sheet l Aug. 27, 1935. R. M, wlL'MoTTEMETHOD OF AND APPARATUS FOR LOCATING A POINT IN SPACE 2 sheets-sheet 2Filed June 26, 195C Patented Aug'. 27, 193s ME'rnoD or AND APPARATUSFonaocA'r- ING A PolN'r IN srAoE Raymond M. Wilmotte, Boonton, N. J.,assignor, by mesne assignments, to Radio Corporation of America, NewYork, N. Y., a corporation oi' Delaware Application June 26, 1930,Serial No. 464,056

17 Claims. (Cl. Z50-11) 'rms invention relates to methods ofv andapparatus for determining the location of a point in space and moreparticularly to methods of and apparatus for determining the location ofaircraft.

Systems of the radio beacon type for guiding aircraft along a line in ahorizontal plane are well known, and it has been proposed to establishan electrical field in space adjacent a landing iield for guidingaircraft to the ground. According to this system, waves are emitted froma directional radiator at or adjacent the landing field and the aircraftis provided with a receiver which includes an instrument for measuringthe intensity of the electrical eld at the aircraft. By holding theaircraft on a horizontal course until the receiver instrument indicatesa. predetermined field strength, and then constraining the aircraft tofollow such a course that the instrument reading remains constant at thepredeter mined value, thev 'aircraft will approach tl ground along asloping line which represents the location, in space, of equal potentialor eld strength. The radio beacon or other appropriate means may beemployed at the' same time for indicating the vertical plane in whichthe aircraft should travel.

This system of guiding aircraft to ground is open to the seriousobjection that it does not afford any indication of the altitude of theaircraft. When landing in a fog or at night without nood illumination,the pilot has no means for determining his relative position upon theequipotential line which he is travelling.

Objects of the present invention are to provide methods of and apparatusto afford a three-dimensional determination of a point in space. Furtherobjects are toprovide a method of and apparatus for guiding aircraft orsubmarine craft along a definite line in space, and for indicating theirposition upon that line. AMore particularly,

objects are to provide methods of and apparatus' for establishing inspace an intersecting pattern between two systems of electrical waves,one system of equipotential lines thus established providing anindication for guiding aircraft to the ground and the second system ofequipotential linesmaiording an' indication of the distance between theaircraft and .the ground.

These and other objects of the invention will be apparent from thefollowing specification when taken with the accompanying drawings inwhich:

Fig. 1 is a diagrammatic view illustrating the location, on a verticalplane, of the intersecting patterns formed in space by two systems ofelec- Fig.- 3 is a ditic View of the equipment carried by the aircraft;

Fig. 4 is a front elevation of one form of indicating device forming apart of such equipment; and

Fig. 5 is a diagrammatic view, similar to Fig.` 1, but on a largerscale, illustrating one method of guiding aircraft to ground.

As indicated in the plan view, Fig. 2, the landing field may be providedwith some form of radio beacon equipment l, 2, for establishing avertical plane, indicated by the broken line 3 of Fig. 2, along whichthe aircraft such as an aeroplane d may be guided to the landing'fleld.

In accordance with the present invention, two directional radiators A, Bare located at opposite sides of the radio beacon plane 3 for emittingcarn rier waves of the same radio frequency but modulated at differentlow or audio frequencies.

As indicated by the diagram, Fig. l, the electrical waves emitted fromthe sources A and B establish an intersecting pattern in space as thetwoelds are not coincident. In Fig. l, the solid lines represent thelocus, in the vertical plane I3, of points of several differentpotentials as established by the source A, and the series -of dottedlines indicate similar equipote'ntial lines established by the source B.

For convenience of description, the'equipotential lines from. source Aare identified by reference numerals 49a to 52a, it being assumed thatthe eld strength from source A along line a,

for example, is such that the indicating instrument on the aeroplanewill read 50 when the aeroplane is at any point along the equipotentialline 50a. The equipotential lines from source B are similarly indicatedas 49h to 52h, inclusive, and it is to be noted that, at any given pointon the ground, the field strength from the two sources is substantiallyequal.

It will be apparent that the two intersecting fields provide a system ofcurvilinear coordinates which affords an absolute determination of apoint in the vertical plane 3 when the respective eld strengths at thatpoint are known. Assuming that the aircraft is provided with appropriateequipment for measuring the intensity of the field strengths of sourcesA and B the pilot can plot his altitude above the ground and hishorizontal distance from sources A and B.

As it would doubtless be inconvenient if not impossible for a pilot toplot his course on a chart such as represented by Fig. 1, apparatus' ofthe type shown in Figs. 3 and 4 may be employed to afford a continuousindication from which the pilot may judge his position with respect tothe landing field.v As indicated diagrammatically Iin Fig. 3, thereceiving and indicating equipment includes a radio frequency amplifier5 that is connectedacrossasuitableantmnasiructm'eiand ground] on theairplane and which works intol a radio frequency rectifier 8. 'Iheoutput from the rectiiier includes both of the modulation frequenciesemployed at sources A and B, respectively, and these low frequency81811818 are passedl to the filter! where they are separated into twochannels, one feeding the source A modulation to the low frequencyrectifier ilo and the other feeding the source B modulation to thelowfrequency rectifier IIb; The rectified outputs from the low frequencyrectiilers pas to separate windings of a measuring instrument kIl toactuate pointers 12a, 12b; respectively, that move over a single scaleI3. Theampliiierandthemeasming'instru-- ment are preferably so designedthat the reading at the centralportion of the scale corresponds to the field strength at an equipotential line, for example, line Sla or 50h,along which the airplane 'istobeguidedtotheground'Ihemeasuringinstrument Ii is preferably provided with a iidu cial mark'Il which extends across the path of travel of both pointers Vat a scalereading corresponding to the predetermined iield intensitywhich thepilot is to employ in landing the airplane.

The position'in space of any given equipotential line may be maintainedsubstantially xed by appropriate control oi. the s ourccs A and IB. Theairplane may,ifdesired.bepmvidedwithan oscillator for checking oradustlng the performance of the receiving equipmmt as the airplaneapproaches the landing eld.

As indicated above, the observed readings of the two ileld intensitiesmay be plotted on cur'vilinear coordinates to determine the location ofthe craft, and such aA methodV may be quite feasible in the case ofsubmarine vessels or dirigible aircraft. In general, however, suchplotting of the course of the craft is unnecesary as the pilot may'estimate his position with sumcient accuracy when a double pointermeasuring instrument is approaches the landing iield. In using thissystcm, the pilot will hold an approximately horlzontal course, in theradio beacon plane Y3, until the pointer I2a is opposite the flducialmark Il which coincides with the "50 mark on die scale I3. Since the twoilelds are non-coincident, the position of pointer lZb at the instantthat pointer I2a is opposite the iiducial mark Il, will afford anindication of the altitude of the aircraft, for

example, an aeroplane, when it reaches the equipotentlal line Sla. Thegreater the diii'erence betweenthetwoiieldstrengtha'asindicatedby thenumber of scale divisionsbetweenpointer IIb and the ndueiai mark u, thegreeterthe alu- -tavels along the equipotenthl line 50a, and at tudeof.the aeroplane. The pointerV |2b approaches the flducial mark Il asthe aeroplane a predetermined potion a pointul IIb (pointer Y I2a beingcontinuously at-the 50 scale division)thepilotknowsthathehasrclchedthataltitude at which the aeroplane shouldbe flattened out for landing. I

According to another method, which is illustrated diagrammatically inFig. 5, the pilot may Vhold the plane on an approximately horizontalcourse until the pointers Ila and i2b lie at opposite sides of theflducial mark I4; i. e., until the plane is in the area defined vby theequipotential lines 50a and'itb. Successive positions of the aeroplaneinspace and diagrammatic illustrations of the instrument readings areshown at the transverse planes indicated by broken lines I, II and III.At line I, the plane is midway between eqllipotential lines 50a and.."lllb,A as indicated by the fact that the pointers IZa and |2b -areequidistant from the ilducial mark I4 which corresponds to a fieldstrength of 50. At this point, the plane is directed downwardly and, ifthe theoretical path is accurately followed, the pointers IIa and lfbwill move towards ma'rk I4 at the same rate, i. e., the positive andnegative increments by which they are spaced from ducial mark Il willremain equal to each other as they indicated by line 111, theequpotential linesv a and SIb meet in space at that altitude above thelanding field at which the aeroplane should atten out or level ofi forlanding. 'Ihe pilot is advised of. his arrival at this altitude by thefact that the pointers l2a and I2b. both coincide with the iiducial markat this point on the predetermined travel path. 'I'he sources A and Bare, of course, so-adjusted that this intersection of the 50 potentiallines liesnot only at the desired altitude but at such horizontaldistance from the .decrease in magnitude. -At the transverse planintended landing point that the latter may be reached in normal flightif the plane is leveled off as it passes this intersection.

'I'here will necessarily be some pe A ble latitude in the use of thissystem as-there must be in all systems involving the skill of anoperator and sensitive apparatus which may vary somewhat in itsoperation. If, for example, the pilot has failed to guide the aeroplanealong such a pathJ that the iield strengths or instrument pointerscoincide at the transverse plaine III, but realizes this condition at asubsequent position, i. e., transverse plane IV corresponding to equalfield strength of "52 magnitude, he may then level off for landing ifthe landing eld is of such size that the horizontal distance betweenplanes III and IV may be neglected. Similarly, if the ampliilcation ofthe receiving apparatus falls below the standard value which would bringthe pointers to the ducial mark as the aeroplane reaches plane III, theonly error introduced is in the indication of horizontal position andnot in altitude. 'Landing ilelds are usually of relatively large areaand therefore the pilot may safely land in the intended manner'eventhrough the sensitivity of the receiver has sodecreased that theaeroplane reaches the leveling oif altitude at transverse plane IV andnot,- as the instrument indicates, at plane III.

In the above description, it has been assumed that the aeroplane iscarefully guided along the theoretical or predetermined path which willgive rise to accurately predetermined variations in the Y instrumentreadings. The path actually taken by the aeroplane will usually be onlyan approximatim of'tltue theoretical path, but with sensitive .meamrlnginstruments, the pilot can reduce the meanderings from the intended pathto small and non-important magnitudes. Although flying y conditions maybe so it is impossible tions at the landing field or by the particularaeroplane. The above examples are therefore to be understood asillustrative of the methods which may be employed in guiding aircraft tothe ground when the position of the aircraft is known to the pilot.

For simplicity of explanation, it has been assumed that the two fieldstrengths are equal or approximately equal at that point in space atwhich the aeroplane should level off. This equality of.

the eld strengths is by no means essential so long as the pilot is awareof those predetermined variations in the instrument readings whichcorrespond to the intended path of travel. As it is inconvenient to notethe readings of pointers on two separate instruments, or at twoseparated portions of a single scale, it will usually be desirable todesign the receiving equipment to bring the pointers 12a and i217 intocoincidenceor approximate coincidence for the respective eld strengthsexisting at the critical altitude above ground level. This may bereadily done in the case of unequal field strengths by employinginstrument movements of different sensitivity, or by selectivelyamplifying the energy from the separate sources. The field strengths maybe so related that, as

the aircraft travels along an equipotential line of one eld, theobserved changing values of the other field strength are proportional toaltitude. Or, if desired, the elds may be so related that the change instrength of the second field is greater at low altitudes than at highaltitudes.

The two sources may derive power from a. single or from separateoscillators when the radiated waves are of the same radio frequency butmodulated at diiferent low frequency. If desired, the signals may be ofdiierent radio frequencies modulated at the same or different lowfrequencies, or unmodulated; the receiving equipment being appropriatelydesigned to measure the respective field strengths.

It is therefore apparent that the choice of the intersecting pattern, aswell as the design of the ,indicating instruments affords such latitudethat.

as the' aircraft or submarine vessel is/iioved along a path giving riseto a predetermined variation (which may be zero) in the' measured valueof one field strength, the changing readings of the measa pathwhichgives rise to predetermined variations inathefme'asured magnitudesof vthe'intensity of each of said fields.

2.l The method as ser forth more negtpreceging claim, whereintheaircraft is constrained to Y travel upon an approximately horizontalpath until the respective measured field strengths differ from apredetermined value by increments of equal magnitude but opposite sign,and then moving the aircraft along a. path whichsimultaneousiy decreasesthe magnitude of said increu ments at the same rate, whereby the planetravels along a predetermined line in space', and determiningthe'position of the aircraft on that line by comparison of the magnitudeof the said increments with a predetermined standard.

3. The method as set forth in claim 1, wherein the aircraft is movedalong an approximately horizontal path until the measured magnitude ofone ileld reaches a predetermined value, then moving the aircraft alonga path which maintains constant the measured value of said one field andcauses the measured value of the second field to approach thatpredetermined value, and determining the position of the aircraft uponits path of night by comparison of the difference betweensaidmeasuredliield strengths with a predetermined standard.

4. The method of determining the location of aircraft in space, whichcomprises establishing from the ground two electric fields which form anintersecting pattern in the space where the aircraft is located,measuring at the aircraft the strength of the respective electricvfields, and referring the observed measurements of the respective eldstrengths to a system of curvilinear coordinateswhich represent thelocation on a vertical plane of lines of equipotential of 'therespective fields.

5. The method of facilitating the landing of n aircraft travels along aline predetermined in space, and determining the position of theaircraft upon said predetermined line in space by comparison of themeasured magnitude of the strength of the second eld with apredetermined standard.

6. In guiding air craft to ground at a landing field, the method whichcomprises `radiating radio beacon signals consisting' of two systems ofelec# trical signals which determine a vertical plane of equal signalstrength along which the plane may approach the landing field,establishing an intersecting pattern by propagating two` sets ofelectrical waves in the space through which aircraft may be guided bysaid radio beacon signals, measuring at the aircraft'the ileld strengthof each of said sets of electrical waves, and determining the positionof the aircraft theequal signal strength plane of said radiobeaconsignals by plotting the measuredv field .strengths on a system ofcurvilinear coordinates representing the location in said verticalyplane-of lines of equi- 1 secting pattern, said indicating meanscomprislwhich form an intersecting pattern in the space adjacent saidpath, moving the aircraft. along said path to produce predeterminedvariations in the observed magnitude of the intensity of one field atthe aircraft, and comparing the changing value of the intensity of theother field with a predetermined standard to determine the'distancealong which theA aircraft has travelled along "the field.

'9. The method of guiding aircraft to ground at a predetermined point ona landing field which comprises, establishing an electrical field whichmarks out a path running through the landing point on said field,producing two noncoincident electrical fields of like frequency whichare directive and forman intersecting pattern in the space through'which the aircraft should pass in following said path toward or from thelanding point on said field, measuring at the aircraft the intensity ofeach of 'said fields separately, and causingthe aircraft to move along apath which gives rise to predetermined variations in measuringmagnitudes of the intensity of each of said fields. Y.

10. In apparatus for facilitating the landing of aircraft, thecombination with a radio transmission beacon system located adjacent thelanding field, said beacon having directional trans- -mission meansfore'stablishing a vertical plane along which the aircraft may be guidedas it approaches the landing field, two directional radiating antennaslocated adjacent said landing field and at opposite sides of said radiobeacon, said radiating system having means for radiating carrier wavesforming an intersecting pattern into space, and indicating means on saidaircraft for indicating the strength 'of said intering energy absorbingmeans, a radio frequency amplier, a radio frequency rectifier, a lowfrequency filter and a lower frequency rectifier for rectifying' theenergy from both of said radiating antennas, an indicating meter havingtwo indices to indicate the location of said aircraft with respect toeach of said radiating antennas.

11. Apparatus as set forth in claim 10, wherein the radiating antennaslocated adjacent the landand indicating means on said aircraftforindicating the strength of said intersecting pattern, said indicatingmeans comprising en'ergy absorbing means, a radio frequency amplifier, aradio frequency rectifler, a low frequency filter -and a low frequencyrectifier for each of said radiating antennas, an indicating meterhaving two indices to indicate the location of aircraft within saidintersecting pattern.

13.' In apparatus for facilitating the landing of aircraft, thecombination with a radio'beacon located on a landing field forestablishing a vertical plane for guiding said aircraft to said landingfield, two directional radiating antennas located at equal and oppositesides of said radio beacon foremitting carrier wavesv of the same radiofrequency but modulated at different audio frequencies, forming anintersecting pattern in space wherein `the aircraft travels, indicatingmeans located on said aircraft, said indicating lmeans comprising energyabsorbing means, a

radio frequency amplifier, a radio frequency rectier, a low frequencyfilter and a low frequency rectifier for rectifying the energies of eachof said antennas, an indicating meter to indicate the location of saidaircraft with respect to said radiating antennas.

14. Iii apparatus for facilitating the landing of aircraft at a landingeld, said apparatuscomprising a directional beacon to establish avertical plane for guiding said aircraft, said beacon having two fixedcrossed loops, each loop energized by separate generators, two directiveradiating Vantennas located at equal and opposite sides of said radiobeacon for emitting carrier waves of the same lradio, frequency butmodulated at different audio frequencies, forming an intersectingpattern in space wherein the aircraft travels, indicating means locatedon -said aircraft, said indicating means comprising energy absorbingmeans, a radio frequency amplifier, a radio frequency rectier, a lowfrequency filter and a low frequency rectifierfor rectifying theenergies of each of said antennas, an indicating meter to indicate thelocation of said 'aircraft with respect to said radiating antennas.

15. In apparatus for facilitating the landing of aircraft, thecombination with a radio transmission beacon system located at thelanding field, said beacon having directional transmission means forestablishing a vertical plane along winch the aircraft may beguided asit approaches the landing field, two directional radiating antennaslocated at` or adjacent said landing ileld and at opposite sides of saidradio beacon, said radiating system having means for radiating carrierwaves forming `an intersecting pattern into space, and indicating meanson said a raft for tern, said indicatingmeans comprising energyabsorbing means, a radio frequency amplifier, a radio frequencyrectifier, a low, frequency nlter and a low frequency rectifler forrectifying the energy from both of said radiating antennas, anindicating meter having two indices to indicate the location of saidaircraft with respect to each of said radiating antennas.

16. Apparatus as set forth in claim 15, wherein the radiating antennaslocated at the landing field, comprise antennas which are substantiallysymmetrical about a vertical axis.

17. In apparatus for facilitating the landing of aircraft, thecombination of a single radiating .indicating the strength of saidintersecting patf means for establishing afvertical plane along.

which the aircraft may be guided as it approaches the landing' field,said single radiating means beingY located at the landing eld, twodirectional quency filter and a low frequency rectifier for each I ofsaid radiating antennas, an indicating meter having two indices toindicate the location of aircraft within said intersecting pattern.

RAYMOND M. WIIMO'I'I'E.

